Diamond Kata in (newb) Clojure

diamond.clj

(def alphabet (map #(str (char %)) (range (int \A) (inc (int \Z)))))

(defn outside-spaces
  [letter letters]
  (loop [[current-letter & rest] letters
         position 0]
    (if (= current-letter letter)
      position
      (recur rest (inc position)))))

(defn print-character
  [letter position]
  (print (apply str (repeat position " ")) letter))

(defn direction
  [growing]
  (if growing
    inc
    dec))

(defn print-half-triangle
  [letters expanding max-spaces]
  (let [start-row (if expanding 0 max-spaces)]
    (loop [[current-letter & rest] letters
           current-row ((direction expanding) start-row)]
      (do 
        (print-character current-letter (- max-spaces current-row))        
        (when (not (= current-letter "A"))
          (print-character current-letter (- (* 2 current-row) 4)))
        (println) 
        (when rest
          (recur rest ((direction expanding) current-row)))))))

(defn print-triangle
  [letter]
  (let [all-letters alphabet
        max-spaces (inc (outside-spaces letter all-letters))
        letters (take max-spaces all-letters)]
    (print-half-triangle letters true max-spaces)
    (print-half-triangle (rest (reverse letters)) false max-spaces)))

sample-output.txt

clojure-noob.core> (print-triangle "L")
            A
           B B
          C   C
         D     D
        E       E
       F         F
      G           G
     H             H
    I               I
   J                 J
  K                   K
 L                     L
  K                   K
   J                 J
    I               I
     H             H
      G           G
       F         F
        E       E
         D     D
          C   C
           B B
            A
nil
clojure-noob.core> (print-triangle "D")
    A
   B B
  C   C
 D     D
  C   C
   B B
    A
nil
clojure-noob.core> (print-triangle "D")
    A
   B B
  C   C
 D     D
  C   C
   B B
    A
nil